DNA, Structures And Replication Flashcards by Hannah Knowles

How do we know DNA is the molecule of life

Griffith
Avery
Hershey and chase
Experiments in 1920-50

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How is DNA structured

Antiparallel strands form double helix
Sugar phosphate backbone
Base pairs join complementary strands by hydrogen bonding

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What are the complimentary base pairs of DNA

Adenine with thymine

Guanine with cytosine

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What is a nucleotide

Base
Sugar
And phosphate

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What are the differences between base pair bonding

2 bonds between adenine and thymine

3 bonds between guanine and cytosine

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What is the larger scale packing of DNA

Tightly coiled around histones to form chromatin with tightly coiled ones brain more active genes

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How is DNA semiconservative

Each new double stranded molecule contains an original template strand and a newly synthesised complimentary strand

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How is DNA synthesised

Starts at Origin of Replication
Utilises dynamic structure of the replication fork
At the replication fork:
Helicases unwind double strand
Single strand binding proteinase stabilise denatured DNA
DNA primase synthesises RNA primer allowing replication to start
DNA polymerase carries out the elongation of the new strand of DNA, formed by the complimentary base pairing to the template strand

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What are the two strands of DNA

Leading and lagging strands

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What direction does DNA synthesis happen in

5’ to 3’ so requires a free 3’ OH to add on from

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What are Okazaki fragments

Short pieces of new DNA made on the lagging strand, sealed by DNA ligase

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What do the two types of DNA polymerase do

DNA polymerase 1 replaces the RNA primers with DNA

DNA polymerase 111 adds new nucleotides to the new strands of dna

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How are errors in replication amended and what is the resulting error frequency

DNA polymerase has a 3’- 5’ editing function to remove incorrectly inserted bases
This reduces error frequency to around 1 in 10^7

Other enzymes check too and reduce overall error frequency to 1 in 10^9

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What causes mutations in DNA

Arise spontaneously due to errors in replication

Induced by DNA damage such as radiation damage or chemical

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What are mutagens

Agents which induce mutations

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What are the different types of gene mutation

Base substitution
Deletion of bases
Insertion of bases
Rearrangement of bases

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What are the consequences of DNA mutation

Can be inherited if in germ cell

In somatic cell, could lead to cancer specifically of in stem cells

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How can DNA be repaired

Base excision repair: proteins cut out damaged bases
Nucleotide excision repair: cut out sections of damaged DNA strand
DNA polymerase 1 replaces DNA by copying intact strand and DNA ligase seals it

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What is a Barr Body

women inactivate one copy of their X chromosome in each cell and it is pushed to the edge of the nucleus

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What is synteny

Where long strands of DNA sequences are present in the same order across species

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What is translocation and what can it cause

Chromosome breakage and reforming

Can cause: disease, cancer, developmental abnormalities and can be inherited

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What does Xist do?

A regulatory RNA that switches off a copy of the X chromosome in XX cells

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What are exons and introns

Exons are coding sections of pre-mRNA

Introns are regions which are spliced out of pre-mRNA

What are genes used for

Transcribed into Structural RNA or regulatory RNA

Transcribed into mRNA which is translated into proteins

May not contribute to making us, but are remnants of past events

What is a retrovirus

RNA virus which infect cells and have reverse transcriptase which allows them to revert to DNA and join with our genome upon infection

What are pseudogenes

Sequences that are common with functional human genes but are non-functional

What are VNTRs

Variable number tandem repeats | Short sequences which are repeated multiple times

What are SNPs

Single nucleotide polymorphisms

What is a polysome

An RNA molecule that is covered in ribosomes

What are lysosomes

Full of degradative enzymes which degrade certain molecules imported into the cell and old or damaged cellular components

What do the ER and Golgi apparatus do

Various processes including the packaging and secretion of proteins

What are the characteristics of mitochondria

The sites of energy generation in the cell by burning fuel to make ATP Small circular chromosome inside them Inherited mitochondrial DNA from mother

What is a TATA box

Promoter region to initiate transcription Short run of thymine and adenine 25 base pairs before start of transcription

How is transcription initiated

Promoter region -> transcription factors bind -> RNA polymerase II binds-> some transcription factors disassociate -> transcription begins

What is the difference between eukaryotes and prokaryotes

No nucleus in prokaryotes Prokaryotes have polysistzonic rna which can code for multiple proteins in one strand of RNA sequence

What does the 5’ cap do

Protects the mRNA from degradation Helps with transcription

How does a eukaryotic mRNA look

5’ cap -> non coding sequence -> coding sequence -> non coding sequence -> polyA tail

What is polyadenylation

Transcription continues past the point where one or more poly A sequences are present, then stops mRNA is then cut near the poly A sequence and a poly A tail is added

What is splicing

Removal of intronic sequences from pre-mRNA

What are locus control regions

Isolated promoter regions far away from the desired gene

What are the three stop codons

UAA UAG UGA

What is the start codon

AUG methionine

What forms the Rough Endoplasmic Reticulum

membranes with bound ribosomes

What are the two types of ribosomes

cytosolic | membrane-bound

How is the translated sequence signalled to be a secretory protein

first part of sequence is a stretch of around 20 hydrophobic amino acids this is a signal sequence

Why do ribosomes then bind with to the endoplasmic reticulum

signal recognition particles bind to the signal sequence, causing the ribosome to dock to the ER

What its the result of ribosome binding to the ER

the newly synthesised protein is fed through a channel into the lumen of the ER as it is translated, the amino terminal signal sequence is usually cut off

What happens with transmembrane proteins

Translation/ translocation continues until a stretch of ~20 consecutive hydrophobic amino acid is made ( a transmembrane domaine) This is embedded in the membrane, The ribosome continue to make the rest of the membrane in the cytosol

What happens in the ER

Disulphide bridges form | Sugar side chains added

What happens in the Golgi apparatus

Some ER sugars are trimmed and replaced

How are mitochondrial proteins made

deposited in cytosol post-translational import Chaperone binds to protein to prevent folding allowing it to be posted into mitochondria mitochondrial targeting sequence at end of protein to promote import into mitochondria

What are TOM and TIM of the mitochondria

Two channels which the protein destined for mitochondrial matrix is threaded through Translocase of the outer membrane (TOM) Translocase of the inner membrane (TIM)

What is cancer

A group of diseases Solid tumours and leukaemias Disease of body's own cells

What is are key features of cancer at the cellular level

uncontrolled cell division change in morphology dedifferentiation of cells Cell migration into adjacent and distant tissues

What is the progression through cancers for cells

Normal cells -> hyper proliferative cell population -> early adenoma -> late adenoma -> carcinoma

What are the three types of environmental factors that can cause cancer

Biological chemical physical

What does an epidemiology study show

That a chemical is carcinogenic in human | Looks for an association between the exposure and cancer